How to prevent solidification of mastic in nozzles

Using mastic or adhesives in cartons or cartidges that are squeezed out by a handgun, the nozzle is of paramount importance.

Problem is, going back several days, weeks, or months later, the mastic has gone hard in the nozzle. It’s often fine still inside the gun, but the nozzle, even if it had a screw-on cap, is full of solid, which often won’t come out happily. Silicone, as it stays malleable, is the only one to easily remove, so the nozzle gets re-used, but what ways are there to ensure any nozzle doesn’t just fill, solidify, and get thrown away?

This isn’t a problem for tradesmen, who will get through many cartridges a week, so will use the same nozzle on the next tube, thus ending up with several spare unused.